When Lynn Patterson resolved to lose weight early this year, she took a hormone normally associated with pregnancy, not dieting.

The 53-year-old Catonsville nurse went on the hCG diet, named for human chorionic gonadotropin, a hormone that is produced naturally in pregnant women and often used in fertility treatments to trigger ovulation.

Promoters of the diet say hCG suppresses the appetite, making it easy to stick to a diet of just 500 calories a day. They also say it helps the body burn fat while retaining muscle. Patterson said the plan helped her lose 58 pounds in just four months.

"I'm probably the smallest I ever remember being," said Patterson, who dropped from a size 20 to a 12. "You want to go shopping again for clothes. That part's just really great. You just have to keep thinking about that when you want that big old dessert."

While Patterson is entirely sold on the benefits of hCG, many medical experts doubt that the hormone is helpful. And they worry that 500 calories a day amounts to a starvation diet, which can cause heart damage and other health problems. The potential health risks could be higher in Maryland and other states, where telemedicine laws allow doctors to prescribe the drug, derived from the urine of pregnant women, with just a telephone consultation, experts warn.

The diet was developed in the mid-1950s by Dr. A.T.W. Simeons, a British physician. It has come in and out of vogue since then, with its current comeback fueled by the availability of hCG online.

While the number of people on the hCG diet is not known, the American Society of Bariatric Physicians reported a surge in its popularity last year, when the society also took a formal position against it on the grounds that it was not effective and did not provide sufficient protein.

"I think it is something that is not well-founded in science," said Dr. Larry Cheskin, medical director and founder of the Johns Hopkins Weight Management Center at the Bloomberg School of Public Health. "Anyone who goes on a 500-calorie diet will, of course, lose a lot of weight quickly, although probably not safely."

Even with a patient under medical supervision, Cheskin said, he would rarely recommend a diet of less than 800 calories a day. About 1,200 calories would be more typical, he said.

Cheskin also doubts that the hormone, which some dieters inject themselves with and others take orally, has any effect on appetite.

"Is the injection working, or is it a placebo effect?" he said. "I've seen people who have tried it, [but] maybe this is a biased sample. If they're coming to me, it didn't work."

Patterson decided to give the diet a try after a friend had success with it. She had put on about 40 pounds over a four- to five-year period when she was busy working and caring for her ailing mother, who died about a year ago.

"I was caring for Mom. I would eat fast food a lot and didn't care," said Patterson, the mother of three grown daughters.

In early January, she started taking the hormone orally twice a day, adhering to a 500-calorie diet.

"The first week or so I was [hungry]," she said. "It was hard to adjust." But eventually, she said, she wasn't battling hunger so much as ennui.

"It's a very boring diet," she said.

In the morning, she had only water and coffee. Lunch and dinner were always the same: 31/2 ounces of lean protein (steak, chicken or white fish), one cup of a vegetable, a single piece of Melba toast and a serving of fruit, which could be a whole apple or orange, a cup of strawberries or half of a grapefruit.

Dull as it was, she said, the diet allowed her to drop pounds. Patterson used to consume "probably 3,000 calories a day, maybe 3,500," mostly in the form of fast food. She doubts she could have slashed that to 500 calories without the hormone.

"I've probably been on every diet known to mankind, and this one just works for me," she said.

But Patterson also said that her husband, Rex, lost weight without taking the hormone or consciously going on a diet simply because she rid the house of junk food and started preparing more healthful meals for the two of them.

"My husband, because I didn't have stuff in the house, he lost 30 pounds," Patterson said. "I took away his soda, switched from lemonade to Crystal Light, tuna sandwiches instead of burgers. And he was not on the diet. We're eating at home."

To Cheskin, that suggests it's good eating habits, not hCG, that can work magic.

"So is it the hCG, or is it the fact that when you're committed and you want to lose weight, you make changes?" Cheskin said. "Any treatment you give, you always want to have a controlled comparison, and we don't have that for hCG. There are no studies that give some people hCG and some people a placebo."

The doctor who put Patterson on the diet is Dr. Fred Bloem, a holistic physician in Olney. He has been prescribing hCG to dieters for about four years and has had "hundreds of patients following the diet," he said.

"The key is to use a small amount of hCG in combination with a specific low-calorie diet, and when you do it, the hCG somehow targets the abnormal fat deposits," he said. "As it happens, patients lose weight very quickly, on the order of half to 1 pound a day."

Bloem said the protocol is not a starvation diet.

"Starvation diet, when you do that, you won't be a happy camper," he said. "You'll be hungry and ... start to look gaunt, lose structural fat in the face, lose muscle mass. ... The hCG somehow targets and mobilizes the abnormal fat deposits and makes it available to the rest of the body as a source of energy."

In a study titled "There they go again: hCG and weight loss," West Virginia University researchers found no "physiologic basis for the use of hCG or any proof of immediate or long term benefit. … Despite these facts, this form of therapy has achieved a resurgence in popularity. The difference today is that patients no longer have to rely on health care providers to prescribe their medications since internet sites allow them to obtain medications 'on line.' "

Diet Doc, an hCG weight-loss program based in Seattle, has a doctor prescribing the drug to about a dozen Marylanders after telephone or Skype consultations, said Julie Wright, president of the company. The company cannot do that in states such as New York, which requires prescribing doctors to see patients face-to-face.

The cost of the diet through Diet Doc is $399 for the first month, and $240 a month after that.

Cheskin, already a skeptic of the hCG diet, takes an even dimmer view of following it under long-distance medical supervision. Telemedicine has its place, he said, such as allowing a patient with a rare condition to consult with a distant specialist.

"That's a specific expertise," he said. "If you're talking about the kind of relationship that is important to people seeking to change their lifestyle, basically, then you probably would do better with someone that you can communicate directly to."